Up to now, a motor control device has been known which detects a temperature of a board on which a control unit for controlling energization of an electric motor is mounted by a temperature sensor, and changes a current limit value or the like according to the detected temperature.
For example, in a device disclosed in JP-A-2004-82757 (Patent Literature 1), two temperature sensors are provided on a board and a heat sink. The device compares detected temperatures detected by the temperature sensors with a predetermined upper limit value and a predetermined lower limit value to determine whether there are an upper limit value failure and a lower limit value failure of the temperature sensors, or not. In addition, when an estimated temperature estimated from a current flowing through an electric motor is rising, the device compares a change in the detected temperature with a change in the estimated temperature, to thereby determine whether there is a fixation failure of the temperature sensor, or not.
The device of Patent Literature 1 individually determines whether there is a failure in each of the temperature sensors, or not. However, in individual determination, even if each temperature sensor is not determined to be abnormal, a deviation exceeding a predetermined temperature difference may occur in the detected temperatures of the two temperature sensors in some cases. In such a case, at least one of the temperature sensors is considered to be abnormal, but it is unknown which temperature sensor is abnormal.
For example, the detected temperature detected by the temperature sensor is used as temperature information for a temperature information processing unit to perform a predetermined process. If the detected temperature detected by an abnormal temperature sensor is used, an error may occur in processing by the temperature information processing unit. In the present specification, “a state in which the detected temperatures of two temperature sensors deviate from each other beyond a normal deviation threshold and which of the temperature sensors is abnormal cannot be identified” is defined as “outside a normal range”. In the conventional art of Patent Literature 1, there is no disclosure of an abnormality in which the detected temperatures of the two temperature sensors deviate from each other beyond a predetermined temperature difference and a concept of “outside the normal range”. Therefore, in such a case, there is a problem that the detected temperature used for processing by the temperature information processing unit is not appropriately selected, and the reliability of the processing by the temperature information processing unit is lowered.
Patent Literature 1: JP-2004-82757-A